1. Field of the Invention
The present invention relates to a resin molded article used as, for example, an external automotive trim. More particularly, it relates to a chipping-resistant resin molded article such as, for example, one which may be attached to the undercarriage of an automobile, such as a rocker molding, a side mud guard or the like.
2. Description of Relevant Art
In improving the efficiency in fuel consumption of an automobile, the reduction of the weight of the body itself is effective. In the weight reduction of the body of an automobile, there is a predominant tendency that plastic or aluminum is used as a material for the body in place of an iron plate, i.e., a conventional material. Owing to the problem of recycling, employment of polypropylene composites (PP composites) is increased in parts of the so-called undercarriage, such as bumpers, rocker moldings, side mud guards, etc.
In a resin molded article such as a rocker molding, a coating layer, such as a primer and a top coat, conventionally used for improving the appearance and protecting the molded article is formed on the surface of the main body of the molded article which is most often made of a polypropylene (PP) or a urethane material. The conventional coating layer is composed mainly of a polyurethane type resin and has a thickness of approximately 30-50 .mu.m.
During the operation of an automobile, the above described parts of the body undercarriage commonly receive an impact of pebbles or gravel which is sent flying by the automobile. Therefore, peeling of the coating of the undercarriage parts or damage to the material itself may be caused, so that their appearance tends to be greatly injured. This common problem is generally referred to as chipping caused by flying stones, however, one skilled in the art will appreciate that such damage may be caused by other projectiles, of which stones are only one example.
In the case of prior art, when a flying stone collides with the previously described coating layer, at a high speed, the conventional coating layer cannot completely resist the impact force and the flying stone partly reaches the main body of the molded article. Consequently, the coating is partly peeled, or the main body of the molded article is injured by the flying stone. Thus, the appearance quality of the resin molded article may be deteriorated.
For the undercarriage, the urethane material is better than polypropylene but expensive and not recyclable.
For coping with these and similar disadvantages conventional procedures have entailed increasing the thickness itself of the coating layer. But, since formation of a coating layer having a thickness larger than a usually predetermined thickness is technically difficult, and such an increased thickness increases costs greatly, such conventional remedies are not generally feasible.